This invention relates to plasma generating apparatus and to processes for operating such apparatus.
Plasma discharges are extensively used in various manufacturing processes such as:
Fabrication of semiconductor devices. PA1 Etching of plastic films for ink adhesion PA1 Deposition of layers on plastic roll goods to reduce oxygen and water vapor diffusion for flexible packaging PA1 Etching and coating fibers and tows (bundle of fibers) to improve adhesion in composite materials or materials such as tire cords. PA1 Etching and deposition on the inside of plastic bottles for increased hermeticity PA1 Etching and deposition on parts to reduce corrosion
For example, a semiconductor substrate is disposed within an evacuated chamber coupled to a source of plasma. By appropriately biasing the substrate, the plasma is coupled to the substrate for ion bombarding the substrate, for etching patterns in the substrate, or depositing ions on the substrate to grow layers of selected materials thereon.
The present invention has particular utility with (although not restricted to) apparatus and processes described in U.S. Pat. No. 4,918,031, issued to me (Johnson), Flamm and Ibbotson on Apr. 17, 1990, the subject matter of such patent being incorporated herein by reference.
This patent discloses a plasma generating apparatus comprising an outside, cylindrical enclosure of metal, an internal helical coil, and an internal, open-ended tube of insulating material within the coil and concentric therewith. A low pressure gas is passed through the tube and ionized by high intensity electric fields generated within the tube by the coil. The ions, radicals, atoms, plasma fragments, or gas phase combined species of the plasma are used to process workpieces, e.g., semiconductor substrates disposed adjacent to an exit end of the tube or within the tube itself.
The patent also discloses the use of a longitudinally split, metallic shield disposed internally of the coil and surrounding the internal tube, and explains that the shield "is useful to adjust plasma species concentrations by application of a bias or to shield the plasma region from radial electric fields." However, except for schematically illustrating the split metallic shield and describing its function in the above quoted statement, the patent provides no significant disclosure concerning its details or use.
I have discovered, however, that the use of internal metallic shields provides important advantages in plasma apparatus of the type described in the patent, and the present invention provides novel shielding arrangements and novel processes for operating apparatus, including such shielding arrangements.